1. Field of the Invention
The present invention relates to a printer and a method of controlling the printer and, more particularly, to a technique effective in improving the printing speed of a printer for printing on pages of a passbook used in a service offered by a financial institution, a bunch of slips formed of sheets of carbon paper or pressure-sensitive paper, etc.
2. Background Art
A printer used as a computer system output device has a printing head with which characters or images are printed on a printing medium such as paper, a mechanism (feed mechanism) for feeding the printing medium, and a control circuit for controlling the printing head and the feed mechanism. The printing head moves in a direction perpendicular to the direction in which the printing medium is fed. With the printing head thus moving, one line of characters or a portion of an image corresponding to one line is printed. After printing of one line, line feed of the printing medium is performed by the feed mechanism, the steps of printing one line and performing line feed are repeated to perform printing on one page.
If the printing medium is limited to ordinary printing paper, a printer can be constructed basically in the above-described manner since the allowable paper thickness can be restricted. However, if a printing medium not uniform in thickness and having a large maximum thickness is used, it is necessary to devise means for constantly maintaining the distance (gap) between the head and the printing medium even when the medium thickness changes. That is, in the case of printing on a bankbook used as a printing medium, it is impossible to constantly maintain the gap between the printing head and the printing medium by simply feeding the printing medium with the feed mechanism while maintaining the printing medium in a state of facing the printing head. Also, in the case of printing on a printing medium not uniform in thickness along the direction of moving of the printing head, e.g., a passport or a bankbook in a country other than Japan, on which characters are printed laterally, and which is opened along a left-right direction, or on a printing medium having a fold, a mechanism is required which constantly maintains the gap by continually moving the printing head or the platen so that the gap is constant while the printing head is moving in the printing direction.
If the gap varies or an air layer exists due to a fold as described above, a reduction in printing quality results. The following are two typical methods conventionally used to cope with this problem. In the first method, an abutment bar having an opening in correspondence with a printing area is disposed between the platen mechanism and the printing head, and a printing medium is inserted between the abutment bar and the platen and is pressed against the abutment bar by the platen mechanism during printing with the head. In this case, the printing surface of the printing medium is maintained flush with the lower surface of the abutment bar since the surface of the printing medium is pressed against the abutment bar by the platen mechanism. The printing position of the head is selected in advance in correspondence with the lower surface of the abutment bar. Thus, the desired head gap is maintained to ensure good printing quality.
In the second method, a roller capable of rolling along the direction of moving of the head is disposed and a printing medium is inserted between the roller and the platen mechanism. The platen mechanism is arranged so as to always apply a force for pressing against the roller. The roller thereby presses the printing medium to constantly maintain the gap by removing an air layer even if the printing medium has a fold or variation in thickness, thus obtaining good printing quality.
The first method described above, however, requires making the printing medium movable by releasing the pressing force of the platen bar before the feed mechanism starts operating to effect line feed of the printing medium. That is, at the time of line feed of the printing medium, it is necessary to perform the steps of releasing pressing by the platen bar and thereafter making the platen bar press the printing medium. The time for the line feed operation is increased if these steps are performed, resulting in an increase in total printing time.
In the case of the second method, line feed of the printing medium cannot be performed when the printing medium is interposed between the head roller and the platen mechanism. That is, if line feed is performed while the printing medium is pressed against the head roller by the platen mechanism, the printing medium is creased or, if the printing medium is carbon paper or the like, a trailing mark is left in a portion pressed against the roller. Creases in the printing medium may cause transfer failure or a reduction in printing quality. Therefore it is necessary that line feed of the printing medium be performed when the head roller is at the end of the platen bar out of the region where it faces the printing medium. If feeding is performed under this condition, it is necessary to move the head to the end of the platen bar even in a situation where the amount of printing of one line is small, that is, the amount of space in one line is large. This means that the time period required for moving of the printing head includes a time period during which printing with the head is not actually performed.
The printing time of the printer is a user""s waiting time. Needless to say, it is desirable to increase operating speed of the printer by considering user"" convenience.
An object of the present invention is to provide a printer capable of maintaining high printing quality and a high printing speed even if the printing medium has variation in thickness or has a fold, and a method of controlling the printer so that the printer has such improved performance.
The present invention will be outlined below. That is, a printer in accordance with the present invention includes a printing head for performing printing while moving over a printing medium, a gap roller capable of rolling along the direction of moving of the printing head, a platen bar placed so as to face the printing head and the gap roller, and a controller for controlling the pressing force of the platen bar applied to the gap roller according to a printing end position of the printing head on the printing medium.
The present invention may be understood as a method for controlling a printer in the above-described manner.
Various other objects, features, and attendant advantages of the present invention will become more fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views.